It is well-known to use humidifying systems which employ steam generators. The boiling of the supply water to generate steam is advantageous because bacteria present in the supply water are killed and minerals present in the supply water tend to remain in the evaporation tank. Thus, the steam fed into the heating, ventilating and air conditioning system is clean and sterile.
The supply water in such devices is the usual local supply water which invariably contains insoluble mineral salts, such as calcium carbonate. Thus, over time, deposits of dirt, dust, lime and other minerals accumulate on various interior surfaces of the steam generator, including the heat exchange surfaces and walls of the evaporation tank. This reduces the efficiency of energy transfer from the heat source to the water. Frequent removal of accumulated, adhering, mineral deposits is required. The task of removing accumulated mineral deposits is at least bothersome and it may be quite difficult.
It has been suggested to drain periodically some of the water in the evaporating tank in order to reduce the build-up of mineral concentration therein. This is not fully satisfactory because a relatively large quantity of water is circulated through and is discarded from the evaporation tank during operation. This mode of operation is unsuited for areas where water conservation is desireable. Moreover, the additional tanks, pipes, valves, etc. that are required increase the cost of the installation and, over time, mineral deposits may adhere to them and require cleaning.